Bottles, cans and carriers containing bottles or cans are commonly packaged for shipment in tray cartons, which comprise a bottom panel foldably connected to relatively short side and end panels. In the packaging operation tray carton blanks are fed to a continuously operating packaging machine which moves the blanks at high speed and at the same time introduces the articles to be packaged and forms the cartons from the blanks.
Part of the carton forming operation consists of folding the end panels of the blanks up against end panel flaps and gluing the end panels to the flaps. This is conventionally done by employing static folding rails to gradually fold the end panels up into proper position as the filled carton blanks move by. Glue is applied just prior to the folding operation so that the end panels can be brought into contact with the end flaps before the glue dries. When the machine stops running, however, the carton in the closing and sealing station at the time is not fully sealed because the carton will not yet have reached the station where the end panels are brought into contact with the end flaps. By the time the machine starts up again the glue will have dried and the carton will not hold together.
This problem has been recognized in the past and attempts have been made to solve it. For example, U.S. Pat. No. 3,504,478, issued Apr. 7, 1970 to Dieter, discloses separate closers or plates for pushing the end panels up against the end flaps when the pnuematic circuit involved is actuated. At the same time the frame that holds the end flaps in their folded position must be moved away in order to make room for the closer plates to operate. These actions take place before the end panels have begun to be folded up toward the end flaps. This arrangement requires extra equipment which is relatively bulky and which tends to require maintenance itself. Further, it takes up space on the machine which otherwise could be used for the basic tasks of feeding and fabricating the tray cartons.
Another approach to the problem is disclosed in U.S. Pat. No. 4,562,687, issued Jan. 7, 1986 to Green, Jr., which discloses the use of folding plates having a component of movement in the direction of travel of the tray cartons. The positive folding action employed adheres the end panels of each tray carton to the end flaps, including the carton at the sealing station at the time of a machine shutdown. While this approach eliminates the problem discussed above, it requires moving parts to carry out the normal folding and sealing process and as such is subject to more equipment maintenance and equipment failure. Further, greater machine speeds are possible with stationary rail folders.
It would be desirable to provide means for sealing the end panels to the end flaps in a simple yet efficient manner which can readily be incorporated in a conventional tray carton packaging machine.